What is the trigeminal neuralgia?
Trigeminal neuralgia (TN, tic douloureux) is a disease characterized by pain in the distribution of the trigeminal nerve in the face.
How does the trigeminal neuralgia develop?
Trigeminal nerve is the only nerve providing sensory innervation to human face. Sensory signals from the skin like warm/cold, touch, pressure, vibration and pain reach the brain via this nerve. Trigeminal nerve sprouts out to three main divisions which destinate to forehead, cheek and jaw. These three branches unite into a single nerve which enters the brainstem after passing a short distance in the subarachnoid space.
This space is the passing location for nerves entering to and exiting from the brain as well as arteries and veins providing blood flow to and from the brain. Sometimes a nearby artery or vein may wrap around the nerve and compress it. Since the pressure inside the artery and vein is not constant and changes with heartbeats the pressure is pulsatile in nature. Therefore, individual nerve fibers suffer and get irritated resulting in trigeminal neuralgia.
What are the symptoms of trigeminal neuralgia?
Typically, TN is manifested by sudden, intensive, excruciating, sharp, electric or thunder-like painful attacks lasting a few seconds (tic douloureux). These painful bursts can be precipitated by speaking, laughing, touching, eating, tooth brushing, i.e. anything stimulating the trigeminal nerve. This form of the disease is called typical trigeminal neuralgia or type 1 (TN1).
Contrary, type 2 (TN2) or atypical form is characterized by long-lasting dull pain. One patient may experience both pain types alternatively or superimposed on each other. Usually there is an associated numbness in the affected area but the patients may be unaware of this due to pain.
Usually the pain is exhibited in one of the branches of the trigeminal nerve. Sometimes two or all three branches may be affected. Mandibular branch providing innervation to the jaw and lower teeth is most frequently affected. Maxillary branch, proving sensation to cheek and upper teeth is less commonly affected. Ophthalmic branch, innervating the forehead is the least affected nerve.
How is the diagnosis of trigeminal neuralgia made?
The diagnosis of trigeminal neuralgia is based on clinical presentation. Physical examination is unremarkable but may show hypoesthesia in the distribution of one or more trigeminal nerve divisions.
Currently there are no laboratory or imaging modalities to confirm the diagnosis. In vast majority of cases, the symptoms are very typical and the diagnosis is straightforward. However, in other cases the patients may exbibit confusing pain pattern leading to misdiagnosis and mistreatment. This is especially true for cases presenting with tooth pain. These patients may undergo unnecessary tooth treatment and even extraction.
Although radiological diagnosis of trigeminal neuralgia is not available demonstration of vascular compression is possible with fine, thin-sliced FIESTA or CISS sequence MRI scan. However, one should remember that vascular compression is not always symptomatic and should be correlated with clinical findings for accurate diagnosis. In some cases, the compressing factor maybe a tumor or a benign arachnoid cyst.
What is the treatment of trigeminal neuralgia?
Initial treatment of trigeminal neuralgia is medical. Carbamazepine is the drug of choice and provides pain relief in the majority of cases. Other medications like gabapentin or topiramate may be also helpful in selected cases. The patient should bear in mind that medical treatment does not provide cure and is aimed to interfere with propagation of abnormal signals within the nerve. Therefore, these medications are taken lifelong.
Cases refractory to medical treatment i.e. not responding to conservative treatment should be managed surgically. In some cases, the disease is progressive i.e. after initial success with mediation the pain recurs later on. If compressing factor is a tumor or a cyst the condition is treated with surgical intervention.
The surgical treatment of choice is microvascular decompression (MVD). This procedure is aimed to permanently relieve the pressure from the nerve by separating the blood vessel. Usually a tiny Teflon paddy is inserted in between them to keep two structures apart and provide lasting relief for the nerve.
The procedure is performed under general anesthesia. A small opening in the skull called craniotomy, is performed behind the ear. Then the surgeron works around the cerebellum to find the trigeminal nerve.
The affected nerve is exposed and separated from the compressing artery and/or vein. The Teflon sponge is inserted and left permanently.
The craniotomy is closed and the patients can usually leave the hospital in 1-2 days. Microvascular decompression has high success rate and is considered the best surgical treatment modality for trigeminal neuralgia.